Room pressurization VAV minimum ventilation (CetVavVntCtl11)

Overview

The application function "CET room pressurization VAV ventilation control 11, minimum ventilation" (CetVavVntCtl11) collaborates with the room pressure control application for ventilation purposes. The ventilation rate is selected from a set of configured values based Room Operating Mode and HVAC Plant Mode.

Main Features:

Ventilation rates selected according to occupancy, reflected by Room Operating Mode and Plant Mode.

Ventilation includes transfer air (maybe for airflow tracking instead)
Ventilation monitor
Ventilation alarm
Normalized airflow values

monitor
configuration

Rapid Ventilation – high flow rate driven by command from user or external application.

Function

The AF selects one of the configured values to apply as the current ventilation rate for the room. If the HVAC plant mode is:

Comfort
Pre-comfort
Economy
Protection

The AF applies the corresponding rate.

If HVAC Plant Mode has any other state, the AF selects the ventilation rate according to the Room Operating Mode and the HVAC Room Operating Mode.

In a typical application, room occupancy schedules or occupancy sensors drive the Room Operating Mode and the ventilation rate.

Normalized flow values

The AF includes a configured value for the minimum ventilation rate in each Room Operating Mode. These values may be entered in several numerical representations:

physical volumetric flow units (typically selected method of configuration)
air changes per hour (alternate method of configuration)
airflow volume per unit of floor area (alternate method of configuration)

The user indicates which numerical representation is applied by setting a separate, multi-state configuration value (RVntMinUnit) that indicates the units of the configured minimum flow data. The application calculates the required ventilation rates in physical flow units and writes that data to calculated value objects.

In addition to the monitoring value in physical flow units, the AF calculates 2 normalized flow values for monitoring ventilation.

Air changes per hour: flow rate divided by room volume. (If the configured value of room volume is zero (the default value), set the monitoring value to zero.)
Airflow per unit floor area: flow reate divided by floor area. (If the configured value of the floor area is zero (the default value) the application sets the monitoring value to zero.)

When the ventilation rate data is invalid the reliability of all the ventilation AV’s is set to ‘Unreliable_Other’.

AirFlVnt
Ventilation air volume flow (AirFlVnt) refers to the airflow through the room that dilutes and removes air contaminants. In a negatively pressurized room, this includes supply flow and transfer air (or total exhaust.) In a positively pressurized room, it is only supply flow.

VntVRate
Ventilation velocity rate (VntVRate) is the measured ventilation rate in airflow per unit floor area.

VntAchgRate
Ventilation air change rate (VntAchgRate) is the measured ventilation rate in air changes per hour.

VntAlm
Ventilation alarm (VntAlm) is intended as a real-time indicator to building operators and as a long term indicator, recorded over time and used to verify and improve operation.

SpAirFlVnt
Ventilation air volume flow setpoint SpAirFlVnt) ventilation airflow setpoint based on Room Operating mode. A process value object that can be overridden by an operator or external process.

Compare to AirFlVnt to observe performance.

Feature configuration

Feature selections for "Room HVAC coordination" are accessed via the Application configuration task in the Configuration component.

Feature (AF)	Feature description	Ref.
Monitoring ventilation alarm	None/Active	☑
Trend for ventilation alarm	None/Active	☑

Configuration

Parameters

CAUTION

Ventilation rate(s)

Ventilation rates may be part of the client’s safety program; occupational safety regulations may apply.

Ventilation rates must come from the ventilation engineer’s specification.

Description	Parameter	Default value
Unit for minimum room ventilation ▶ Defines the flow measuring units for the Minimum room ventilation parameters. 1:ft3/min 2:l/s 3:/h 4:m3/h 5:m3/h/m2 6:ft3/min/ft2 7:l/s/m2	RVntMinUnit	4:[m³/h]
Minimum room ventilation for comfort ▶ Donot leave at default - set according to job specification. (Minimum room-ventilation setpoint for Comfort) This is the ventilation rate needed in the room during Comfort mode. Value must come from ventilation engineer’s specifications. May be specified as the "occupied ventilation rate" or as the only ventilation rate for the room.	RVntMinCmf	0
Minimum room ventilation for pre-comfort ▶ Donot leave at default - set according to job specification. (Minimum room-ventilation setpoint for Pre-Comfort; might also be specified as "standby ventilation rate") If Pre-Comfort is not specified, the value for Comfort mode might be used. This helps if the room operating mode is set unexpectedly.	RVntMinPcf	0
Minimum room ventilation for economy ▶ Set according to job specification. (Minimum room-ventilation setpoint for Economy; might also be specified as "unoccupied ventilation rate") If Economy is not specified, the value for Comfort mode might be used. This helps if the room operating mode is set unexpectedly.	RVntMinEco	0
Minimum room ventilation for protection ▶Set according to job specification. (Minimum room-ventilation setpoint for Protection) If Protection is not specified, the value for Economy might be used.	RVntMinPrt	0
Volume of room ▶ The VntAchgRate object (Ventilation air change rate) is calculated based on this parameter, and will be 0 if this parameter is left at default. Note: Volume of the room must be entered if RVntMinUnit is set to /h.	RVlm	0 [m³] 0 [ft³]
Area of room ▶ The VntVRate object (Ventilation velocity rate) is calculated based on this parameter, and will be 0 if this parameter is left at default. Note: Area of the room must be entered if RVntMinUnit is set to m3/h/m2, ft3/min/ft2, or l/s/m2.	RArea	0 [m²] 0 [ft²]
Ventilation alarm limit ▶ Defines how much the ventilation flow can deviate from setpoint before the ventilation alarm activates. The ventilation alarm will activate if the room ventilation airflow is not within VntAlmLm of the room ventilation airflow setpoint for longer than DlyVntAlm. Set according to customer’s need to monitor ventilation rates. Set low enough that normal variation in flow measurements do not trip the alarm, but high enough to notify operating staff if the system is not performing as expected.	VntAlmLm	70 [%]
Ventilation alarm delay ▶ Set according to customer’s need to monitor ventilation rates. In most applications a brief lapse in ventilation will not result in an air quality problem. Set the delay long enough that normal dynamic flow changes do not cause unnecessary alarms.	DlyVntAlm	900 [s]
Volume unit ▶ Defined by selected engineering unit – do not change.	VlmUnit	[m³] [ft³]
Area unit ▶ Defined by selected engineering unit – do not change.	AreaUnit	[m²] [ft²]

Interface

Interface	Description	Type	Ref.	Owned by
SpAirFlVnt	Ventilation air volume flow setpoint	APrcVal	●	-
VntAlm	Ventilation alarm 1:Normal 2:Alarm	BCalcVal	●	-
VntAlmMon	Monitoring ventilation alarm	FtrSel	●	-
TrndVntAlm	Trend for ventilation alarm	FtrSel	●	-
AirFlMinRCmf	Minimum room air volume flow for comfort	ACalcVal	●	-
AirFlMinRPcf	Minimum room air volume flow for pre-comfort	ACalcVal	●	-
AirFlMinREco	Minimum room air volume flow for economy	ACalcVal	●	-
AirFlMinRPrt	Minimum room air volume flow for protection	ACalcVal	●	-
AirFlVnt	Ventilation air volume flow	ACalcVal	●	-
VntAchgRate	Ventilation air change rate	ACalcVal	●	-
VntVRate	Ventilation velocity rate	ACalcVal	●	-

Engineering and commissioning

Users may command the ventilation level and other applications may override it by setting the BA-Object SpAirFlVnt. The object is expressed in physical flow units.

Calculated value objects indicate the minimum flow rates for each room op mode. These values are in physical flow uints, and show the result of calculations based on room volume or floor area.

AirFlVnt, VntAchgRate and VntVRate are used for monitoring.